Process of decomposing thiocyanic acid



Patented Dec. 18, 1934 PATENT OFFICE PROCESS OF DECODgIPOSING THIOCYANICA D Fritz Overdick, Leverkusen/Wiesdorf, Germany,

assignor to I. G. Farbenindustrie Aktiengesellschaft, Frankfort on theMain, Germany N0 Drawing. Application May "14, 1931, Serial No. 537,508.In Germany June 5, 1930 2 Claims. (01. 23-119 The present inventionrelates to a process of decomposing thiocyanic acid, more particularlyit relates to a process of decomposing thiocyanic acid and salts thereofby means of sulfuric acid in the presence of ammonium sulfate and inapparatus being constructed of or lined with chromium-nickel steel.

It is known that thiocyanates are hydrolyzed by means of dilute acids,such as sulfuric acid, phosphoric acid or similar acids or also mixturesof these acids with the production of the.

ammonium salt corresponding to the acid. I This is effected by heatingthiocyanates with these acids advantageously under pressure,totemperatures exceeding 100 C., for example, to 140,

to 180 c.

The reaction proceeds according to the following steps:

or summarized:

This process has however been found to be of the apparatus employedsince almost all the metallic materials coming into question arestrongly attacked by the hot acids or by the thiocyanic acid primarilyproduced. Even the chromium nickel steels which consist of 15-40% of Cr,20- 1% of Ni and up to 1% of C; or 63-25% of Cr, 20 /3% of Ni and up to1% of C; or 18-24% of Cr, 720% of Ni, 2-6% of Cu and 0.1-0.4% of C; or18-30% of Cr, 20-4% of Ni, 24% of Mo and 0.1-0.4% of C, which otherwiseare very resistant to acids have been found not to be durable in theprocess described. v

In accordance with the present invention the attack on the metallicapparatus in the hydrolysis of the thiocyanic acid by means of sulfuricacid is considerably reduced, provided that the reaction is carried outin the presence of ammonium sulfate.

Particularly resistant to corrosion are in this case steels, whichconsist of 18-30% of Cr, 20-4% of Ni, 2-4% of Mo and 0.1-0.4% of C,

as, for instance, a steel having the following composition:

Feresidue Obviously it is not necessary to construct the whole apparatusof this molybdenum steel, it is sufficient to line with this specialsteel those parts of the apparatus coming into contact with thereactionsolution. In the case of apparatus lined with acid resistantmasonry only the fittings-(for example, heating andthermometertubes)-need be constructed 'of molybdenum steel. 1 I

The following example illustrates the invention without restricting itthereto:

ExampZa-A mixture of 3 parts by weight of ammonium thiocyanate, '4 partsby weight of concentrated sulfuric acid and parts by weight of anaqueous solution containing 35-40% of ammonium sulfate is heated forseveral hours to -180 C. in an autoclave consisting of chromium-nickelsteel containing molybdenum. Complete hydrolysis of the ammoniumthiocyanate then occurs with formation of ammonium sulfate and theapparatus is not substantially corroded.

I claim:-

1. In the process of decomposing thiocyanic acid by means of a mineralacid the step which comprises heating the thiocyanic acid in thepresence of sulfuric acid and ammonium sulfate which has been addedbefore the reaction to a temperature between about 100 and C. in anapparatus the corrodable parts whereof consist at least on the surfaceof chromium-nickel steel.

2. In the process of decomposing thiocyanic acid by means of a mineralacid the step which comprises heating the thiocyanic acid in thepresence of sulfuric acid and ammonium sulfate which has beenaddedbefore the reaction to a temperature between 100 and 180 C. in anapparatus the corrodable parts whereof consist at least on the surfaceof chromium-nickel-molybdenum steel.

- FRITZ OVERDICK.

